Interfering near field transducer for energy assisted magnetic recording

ABSTRACT

An apparatus for energy assisted magnetic recording of a storage disk includes a plurality of dielectric waveguide cores configured to receive incident light energy from an energy source and direct the incident light energy to a target, and a near field transducer (NFT) formed at an air bearing surface of a magnetic recording device. The NFT is configured to focus the light energy received from the plurality of waveguide cores and to transmit the focused light energy onto the storage disk surface to generate a heating spot on the storage disk. The NFT includes a plurality of propagating surface plasmon polariton (PSPP) elements configured as plasmonic metal ridges. Each of the PSPP elements has a width approximately equivalent to the width of the heating spot and is disposed above a surface of a single waveguide core in a longitudinal alignment.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 62/010,038 filed on Jun. 10, 2014, which is expressly incorporatedby reference herein in its entirety.

BACKGROUND

High density storage disks are configured with layers of materials thatprovide the required data stability for storage. The magnetic propertiesof the media require a softening when writing to the disk to change thebit state. Energy Assisted Magnetic Recording (EAMR) device or HeatAssisted Magnetic Recording (HAMR) technology provides heat that isfocused on a nano-sized bit region when writing onto a magnetic storagedisk, which achieves the magnetic softening. A light waveguide directslight from a laser diode to a near field transducer (NFT). The NFTfocuses the optical energy to a small spot on the target recording areawhich heats the magnetic storage disk during a write operation.Inefficiencies in the NFT can have a negative impact on the power budgetof the laser diode and the EAMR/HAMR system lifetime. Higher NFTefficiency allows for lower laser power demand, relieving EAMR/HAMRsystem requirement on the total optical power from the laser source, andresults in less power for parasitic heating of the EAMR/HAMR headresulting for improved reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present invention will now be presented in thedetailed description by way of example, and not by way of limitation,with reference to the accompanying drawings, wherein:

FIG. 1 shows a diagram of an exemplary hard disk drive;

FIG. 2 shows a diagram of an exemplary embodiment of a near fieldtransducer formed with two propagating surface plasmon polaritonelements;

FIG. 3 shows a diagram of an exemplary embodiment of a near fieldtransducer with two propagating surface plasmon polariton elements and aplasmonic metal cap.

FIG. 4 shows a diagram of an exemplary embodiment of a near fieldtransducer formed with three propagating surface plasmon polaritonelements; and

FIG. 5 shows a diagram of an exemplary embodiment of a near fieldtransducer formed with a plurality of propagating surface plasmonpolariton elements that is not equal in number to a plurality ofcorresponding waveguide cores.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various exemplary embodimentsand is not intended to represent the only embodiments that may bepracticed. The detailed description includes specific details for thepurpose of providing a thorough understanding of the embodiments.However, it will be apparent to those skilled in the art that theembodiments may be practiced without these specific details. In someinstances, well-known structures and components are shown in blockdiagram form in order to avoid obscuring the concepts of theembodiments. Acronyms and other descriptive terminology may be usedmerely for convenience and clarity and are not intended to limit thescope of the embodiments.

The various exemplary embodiments illustrated in the drawings may not bedrawn to scale. Rather, the dimensions of the various features may beexpanded or reduced for clarity. In addition, some of the drawings maybe simplified for clarity. Thus, the drawings may not depict all of thecomponents of a given apparatus.

Various embodiments will be described herein with reference to drawingsthat are schematic illustrations of idealized configurations. As such,variations from the shapes of the illustrations as a result ofmanufacturing techniques and/or tolerances, for example, are to beexpected. Thus, the various embodiments presented throughout thisdisclosure should not be construed as limited to the particular shapesof elements illustrated and described herein but are to includedeviations in shapes that result, for example, from manufacturing. Byway of example, an element illustrated or described as having rounded orcurved features at its edges may instead have straight edges. Thus, theelements illustrated in the drawings are schematic in nature and theirshapes are not intended to illustrate the precise shape of an elementand are not intended to limit the scope of the described embodiments.

The word “exemplary” is used herein to mean serving as an example,instance, or illustration. Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. Likewise, the term “embodiment” ofan apparatus or method does not require that all embodiments include thedescribed components, structure, features, functionality, processes,advantages, benefits, or modes of operation.

As used herein, the term “about” followed by a numeric value meanswithin engineering tolerance of the provided value.

In the following detailed description, various aspects of the presentinvention will be presented in the context of an interface between awaveguide and a near field transducer used for heat assisted magneticrecording on a magnetic storage disk.

FIG. 1 shows a hard disk drive 111 including a disk drive base 114, atleast one rotatable storage disk 113 (e.g., such as a magnetic disk,magneto-optical disk), and a spindle motor 116 attached to the base 114for rotating the disk 113. The spindle motor 116 typically includes arotating hub on which one or more disks 113 may be mounted and clamped,a magnet attached to the hub, and a stator. At least one suspension arm108 supports at least one head gimbal assembly (HGA) 112 that holds aslider with a magnetic head assembly of writer and reader heads. A rampassembly 100 is affixed to the base 114, and provides a surface for tipof the suspension arm 108 to rest when the HGA 112 is parked (i.e., whenthe writer and reader heads are idle). During a recording operation ofthe disk drive 111, the suspension arm 108 rotates at the pivot 117,disengaging from the ramp assembly 100, and moves the position of theHGA 112 to a desired information track on the rotating storage disk 113.During recording, the slider is suspended by the HGA 112 with an airbearing surface of the slider that faces the rotating disk 113, allowingthe writer head to magnetically alter the state of the storage bit. Forheat assisted magnetic recording, a near field transducer (NFT) on theair bearing surface may couple light energy from a waveguide to producea heating spot on the rotating disk 113 for magnetically softening thebit space.

FIG. 2 shows a diagram of an exemplary embodiment of an NFT 200 arrangedat an air bearing surface (ABS) 210 of a slider which carries a magnetichead assembly. The ABS 210 is the surface of the slider facing thestorage disk 113. As the slider flies over the storage disk 113, acushion of air is maintained between the slider and the disk 113. Asshown, two dielectric waveguide (WG) cores 211, 212 are arranged to eachcarry light energy into the NFT 200 directed toward a common target. Thelight energy may be generated by a common laser diode source (not shown)that may be split in half by a splitter (not shown). The dielectricwaveguide cores 211, 212 may be of equal length to ensure that thecombined energy wave at the ABS 210 is in substantial phase alignmentfor constructive interference and maximum energy emission to the storagedisk 113. Alternatively, dielectric waveguide cores 211, 212 may be ofunequal length such that the incident energy waves may have a particularphase difference that optimizes constructive interference and maximumenergy magnitude at the ABS 210. The two waveguide cores 211, 212 aresubstantially linear and converge at a junction near the ABS 210 at aninterior angle between 0 and 180 degrees, (e.g., approximately 90degrees as shown in FIG. 2). The dielectric material of the waveguidecore 211, 212 may be Ta₂O₅ for example.

As shown in FIG. 2, a plasmonic metal ridge element 201, 202 may bedisposed above each waveguide core 211, 212 in a longitudinal directionalong the center the waveguide core surface. The optical energy from thedielectric waveguide core 211, 212 in proximity with of the plasmonicmetal ridge 201, 202 energizes propagating surface plasmon polaritons(PSPPs) along a surface of the plasmonic metal ridge 201, 202 toward theABS 210. Thus, each plasmonic metal ridge element 201, 202 may functionas a PSPP element. The material of the plasmonic metal ridge element201, 202 may be a gold alloy, for example. Other examples of plasmonicmetals that may be used to form the metal ridge element 201, 202 includesilver or copper alloys. As shown in the cross section, a gap (e.g.,about 20 nm) may exist between the plasmonic metal ridge element 201,202 and the dielectric waveguide core 211, 212. Alternatively, the gapmay be omitted, and the plasmonic metal ridge element 201, 202 maydirectly contact the dielectric waveguide core 211, 212, at least for aportion of the plasmonic metal ridge element 201, 202. The twodielectric waveguide cores 211, 212 and the entire NFT 200, includingthe two plasmonic metal ridges 201, 202, may be encapsulated by asilicon oxide material. The plasmonic metal ridge elements 201, 202 maythus be suspended above the dielectric waveguide cores 211, 212 withinthe waveguide cladding and/or slider substrate material.

The plasmonic metal ridge elements 201, 202 may be configured as shownin FIG. 2, converging at a junction above the junction of the dielectricwaveguide cores 211, 212. The junction of plasmonic metal ridge elements201, 202 may occur on a common plane, or may be formed by overlappingone element over the other element. As shown, a single metal ridgeextension 203 may be formed and configured to be perpendicular with theABS 210, extending from the junction of plasmonic metal ridge elements201, 202. This extension 203 may provide a focal point for the NFT 200energy output at the ABS 210 for heating the target bit space forrecording data. For example, the endpoint of the extension 203 mayfunction as an emitter for the NFT 200 energy output. Alternatively, theextension 203 may be omitted, and the junction of plasmonic metal ridgeelements 201, 202 may be formed at the ABS 210. For example, an NFTenergy output emitter may be formed at the ABS 210 by the exposed metalridge junction at the ABS 210, from which the maximum energy ispropagated across the air cushion and onto the surface of storage disk113. The physical dimension of the emitter (i.e., the width of theexposed junction of plasmonic metal ridge elements 201, 202 or extension203) may be approximately equivalent to the size of the focused heatingspot on the surface of the disk 113. The target size of the heating spotis dependent on the track size as the slider flies over the track, whichmay be about 10-70 nm wide for example. The size of the heating spotalso depends on the distance between the ABS 210 and the disk 113. Thefocus of the heating spot may be optimized by minimizing the gap. Thewidth of the plasmonic metal ridge element 201, 202 may also besignificantly smaller than the width of the dielectric waveguide core(e.g., 300-500 nm). Also, the height of the metal ridge element 201, 202may be about 10-70 nm for example.

The two PSPP element configuration as shown in FIG. 2 may provideapproximately twice as much electrical field magnitude compared with aconfiguration of a single PSPP element arranged perpendicular to the ABS210, driven by a common total input power in the waveguide system. Theconstructive interference produced by the two PSPP elements 201, 202allows improved efficiency of energy delivery from the laser diodesource, which translates to longer service life of the EAMR/HAMR device.To optimize the efficiency of the two PSPP element configuration, eachPSPP element 201, 202 is configured with a length L which is an integermultiple of coupling length Lc from dielectric waveguide core to thePSPP element 201, 202 (e.g., for Lc of 1200 nm, the length of the PSPPelement should be about a(1200 nm) where a is an integer value). Withthe PSPP element 201, 202 having a length L approximately equivalent toaLc ensures that the maximum energy transfer propagates from the PSPPelement 201, 202 at the ABS 210. If the length of the PSPP element 201,202 deviates from aLc, some of the energy wave may be lost to thedielectric waveguide core 211, 212.

The NFT 200 does not have to be limited to two interfering PSPP elements201, 202 as shown in FIG. 2. In an alternative embodiment, N (a positiveinteger) PSPP elements interfere at the ABS, which may provideapproximately N times increase of the electrical field magnitude, drivenby a common total input power in the waveguide system. The value of Ncan increase beyond 2 or 3, until other parasitic interferences withinthe three dimensional layout the EAMR head becomes a limiting factor.For N≧3, the PSPP elements may be arranged in a three dimensionalconfiguration.

FIG. 3 shows an alternative exemplary arrangement for an NFT 300, whichis a variation of NFT 200 with an additional plasmonic metal cap 305. Asshown in FIG. 3, the NFT 300 may include the plasmonic metal ridgeelements 202, 203 coupled to a plasmonic metal cap 305 above. Forillustrative purpose, the plasmonic metal element 305 is depicted astransparent to reveal the fine ridge features 201, 202 below. Theplasmonic metal cap 305 is shown in a semi-circle configuration with astraight edge substantially aligned with the ABS 210. The aligned edgeof the plasmonic metal cap 305 may be recessed from the ABS 210. Thematerial of the plasmonic metal ridge elements 201, 202 and theplasmonic metal cap 305 may be a gold alloy, for example. Other examplesof plasmonic metals that may be used to form the metal ridge elements201, 202 and plasmonic metal cap include silver or copper alloys. Thetwo dielectric waveguide cores 211, 212 and the entire NFT 200,including the plasmonic metal cap 305 and two plasmonic metal ridges201, 202, may be encapsulated by a silicon oxide material.

The thickness of the plasmonic metal cap 305 is not a significant factorin achieving the precise nano-sized heating spot, and therefore thethickness may be configured according to providing adequate heattransfer for controlling the peak temperature in the NFT 300. Theplasmonic metal element 305 configuration is determined by a shape andsize necessary to be coupled with the metal ridge features 201, 202(i.e., a footprint that covers the metal ridge features 201, 202). As anexample, the size of a semi-circle shaped plasmonic metal element 305may be 1000 nm in diameter and greater than 100 nm in thickness. Thesurface of the plasmonic metal cap 305 may be configured to have asubstantially flat surface facing the metal ridge features for coupling,while the opposite surface may be flat, rounded or irregular such thatthe overall thickness is variable. While shown in FIG. 3 as asemi-circle shape, the plasmonic metal cap 305 may be configured inshapes other than a semi-circle, such as a rectangular or polygonalblock.

The NFT 300 does not have to be limited to two interfering PSPP elements201, 202 as shown in FIG. 3. In an alternative embodiment, N (a positiveinteger) PSPP elements interfere at the ABS, which may provideapproximately N times increase of the electrical field magnitude. Thevalue of N can increase beyond 2 or 3, until other parasiticinterferences within the three dimensional layout the EAMR head becomesa limiting factor. For N≧3, the PSPP elements may be arranged in a threedimensional configuration. The plasmonic metal cap 305 would alsoconform to a corresponding three dimensional configuration as beingcoupled to the N PSPP elements from above.

FIG. 4 shows an alternative exemplary arrangement for an NFT 400 havingN=3 PSPP elements. Each PSPP element is formed in a manner similar tothat described above for the two-PSPP element configuration shown inFIG. 4 and described above. The NFT 400 may include a plasmonic metalcap 405 and plasmonic metallic ridge elements 401, 402, 403 arrangedabove each respective dielectric waveguide core 411, 412, 413 as shownin FIG. 4. For illustrative purpose, the plasmonic metal element 405 isdepicted as transparent to reveal the fine ridge features 401, 402, 403below. A gap may exist between each plasmonic metal ridge element 401,402, 403 and the respective dielectric waveguide core 411, 412, 413. Thethree dielectric waveguide cores 411, 412, 413 and the entire NFT 400,including the plasmonic metal cap 405 and three plasmonic metal ridgeelements 401, 402, 403, may be encapsulated by silicone oxide material.The plasmonic metal ridge elements 401, 402, 403 may be configured asshown in FIG. 4, converging at a junction above the junction of thedielectric waveguide cores 411, 412, 413. The junction of plasmonicmetal ridge elements 401, 402, 403 may occur on a common plane, or maybe formed by overlapping one element over the other elements. As shown,a single metal ridge extension 423 may be formed and configured to beperpendicular with the ABS 410, extending from the junction of plasmonicmetal ridge elements 401, 402, 403. This extension 423 may provide afocal point for the NFT energy output at the ABS 410 for heating thetarget bit space for recording data. Alternatively, the extension 423may be omitted, and the junction of the three plasmonic metal ridgeelements 401, 402, 403 may be formed at the ABS 410. For example, an NFTenergy output emitter may be formed at the ABS 410 by the exposedplasmonic metal ridge junction at the ABS 410, from which the maximumenergy is propagated across the air cushion and onto the surface of thestorage disk 113. The physical dimension of the emitter (i.e., the widthof the exposed plasmonic metal ridge junction or extension) may beapproximately equivalent to the size of the focused heating spot on thesurface of the disk 113. This embodiment of NFT 400 may alternatively beconfigured without plasmonic metal cap 405.

The number of PSPP elements may vary with respect to the number ofdielectric waveguide cores. FIG. 5 illustrates an example where two PSPPelements 501A, 501B may be disposed side-by-side above a singledielectric waveguide core 511. Similarly, PSPP elements 502A, 502B maybe disposed side-by-side above a single dielectric waveguide core 512.In this example, NFT power delivery efficiency is increased by fiveinterfering PSPP elements 501A, 501B, 502A, 502B, 503 while using onlythree dielectric waveguide cores 511, 12, 513. As shown in FIG. 5, theNFT 500 may include the plasmonic metal cap 505 disposed above the PSPPelements 501A, 501B, 502A, 502B and 503. This embodiment of NFT 500 mayalternatively be configured without plasmonic metal cap 505.

The various aspects of this disclosure are provided to enable one ofordinary skill in the art to practice the present invention. Variousmodifications to exemplary embodiments presented throughout thisdisclosure will be readily apparent to those skilled in the art, and theconcepts disclosed herein may be extended to other devices. Thus, theclaims are not intended to be limited to the various aspects of thisdisclosure, but are to be accorded the full scope consistent with thelanguage of the claims. All structural and functional equivalents to thevarious components of the exemplary embodiments described throughoutthis disclosure that are known or later come to be known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the claims. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed under the provisions of 35 U.S.C. §112(f)unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

What is claimed is:
 1. An apparatus for energy assisted magneticrecording of a storage disk, comprising: a plurality of dielectricwaveguide cores configured to receive incident light energy from anenergy source and direct the incident light energy to a target; and anear field transducer formed at an air bearing surface of a magneticrecording device and configured to focus the light energy received fromthe plurality of waveguide cores and to transmit the focused lightenergy onto the storage disk surface to generate a heating spot on thestorage disk, the near field transducer comprising: a plurality ofpropagating surface plasmon polariton (PSPP) elements configured asplasmonic metal ridges; wherein each of the PSPP elements is disposedabove a surface of a single waveguide core in a longitudinal alignmentwith the waveguide core; and wherein each of the PSPP elements isconfigured with a width approximately equivalent to the width of theheating spot.
 2. The apparatus of claim 1, further comprising: aplasmonic metal cap disposed above PSPP elements and coupled to the PSPPelements.
 3. The apparatus of claim 2, wherein the plasmonic metal capis configured with a straight edge aligned with the air bearing surface.4. The apparatus of claim 2, wherein the plasmonic cap is configuredwith a thickness sufficient for a heat sink to control peak temperatureof the near field transducer.
 5. The apparatus of claim 2, wherein theplasmonic cap is configured with a variable thickness.
 6. The apparatusof claim 2, wherein the plasmonic cap is configured with a flat surfacefor coupling to the PSPP elements.
 7. The apparatus of claim 1, whereina gap exists between each of the plurality of PSPP elements and thecorresponding surface of the respective waveguide.
 8. The apparatus ofclaim 1, wherein each of the PSPP elements is substantially linear andcomprises a first end and a second end, wherein the first ends of allPSPP elements are connected together at a junction point near the airbearing surface with at least a portion of the junction exposed on theair bearing surface.
 9. The apparatus of claim 8, further comprising aPSPP element extension configured to be perpendicular with the airbearing surface extending from the junction of PSPP elements.
 10. Theapparatus of claim 1, wherein more than one PSPP element is disposedalong at least one of the waveguide cores.
 11. The apparatus of claim 4,wherein the plurality of waveguide cores and corresponding PSPP elementsare configured in three dimensional arrangement with respect to the airbearing surface.
 12. The apparatus of claim 1, wherein the plurality ofPSPP elements provides constructive interference of the incident lightenergy at the target.
 13. A magnetic storage disk drive, comprising: arotatable magnetic storage disk; a laser diode; a plurality ofdielectric waveguide cores configured to receive incident light energyfrom an energy source and direct the incident light energy to a target;and a near field transducer formed at an air bearing surface of amagnetic recording device and configured to focus the light energyreceived from the plurality of waveguide cores and to transmit thefocused light energy onto the storage disk surface to generate a heatingspot on the storage disk, the near field transducer comprising: aplurality of propagating surface plasmon polariton (PSPP) elementsconfigured as plasmonic metal ridges; wherein each of the PSPP elementsis disposed above a surface of a single waveguide core in a longitudinalalignment with the waveguide core; and wherein each of the PSPP elementsis configured with a width approximately equivalent to the width of theheating spot.